The outlawed NLFT ultras may have taken the captives into neighbouring Bangladesh as the border is just five km from the spot, 175 km from Agartala under Dhalai district, the official added.

The state government has asked the Border Security Force (BSF) to take appropriate steps to rescue the hostages — all tribals.

The workers were engaged by a contractor to construct a health sub-centre at tribal-dominated Bhagirath village under Gandachara sub-division.

Troopers of the BSF and Tripura State Rifles led by senior police officials have launched a search operation to rescue the labourers.

Police suspect that the extremists might have kidnapped the labourers for ransom.

The banned NLFT, along with another outlawed outfit All Tripura Tiger Force (ATTF), has been fighting for an independent tribal homeland in Tripura and operates out of neighbouring Bangladesh, which shares an 856-km border with Tripura.